Can anyone point me to where I can find what role adenine plays in coenzymes like nicotinamide adenine dinucleotide (NAD) and flavin adenine dinucleotide (FAD)??

Krebs cycle

krebs... right, oxidation and reduction are the roles that NAD and FAD play but those hydrogens don't come from the adenine. I guess specifically within those reactions what is the role of adenine?

It serves as a some kind of "handle" for enzymes.

I mean, there is a common conserved domain among enzymes using adenosine cofactors (ATP, FAD, NAD etc.) called "nucleotide - binding fold". It binds to adenine or adenosine, respectively. So basically, adenosine part serves as a not-so-specific handle of the cofactor and the active part (nicotinamide, for example) ensures the specifity part of reaction. The reason for this is that nature can design lot of different proteins with specifity to different cofactor just using this single protein fold.